Hepatic Lectins, located at the surface of liver cells, are responsible for receptor-mediated endocytosis of partially deglycosylated serum glycoproteins. My previous studies have resulted in determination of the complete amino acid sequence of the chicken hepatic lectin (CHL). The experiments proposed here are designed to exploit the available information about CHL to understand the function of the receptor in this type of endocytosis. The work proposed covers the following areas: (1) Further strutural studies on CHL, including identifying residues involved in forming the glycoprotein-binding site; (2) Vectorial labeling studies designed to elucudate the arrangement of CHL in the hepatocyte membrane; (3) Analysis of the interaction of CHL with other proteins involved in endocytosis, such as clathrin found in coated vesicles; (4) Investigation of the mechanism of CHL insertion into the membrane, with emphasis on detecting possible biosynthetic precursors; (5) Continuation of amino acid sequence analysis of the rat hepatic lectin, an analogous protein with distinct binding specificity which has been found in preliminary studies to show considerable sequence homology with CHL; and (6) Studies employing immunoelectron microscopy with antibodies to CHL to locate CHL in the plasma membrane and internal organells of the hepatocyte. These studies are designed to exploit the avialability of a pure receptor (CHL) to advance our understanding of the mechanism of endocytosis and the role of complex carbohydrates in biological systems.